Field of the Invention
The present invention relates to a variable valve lift apparatus. More particularly, the present invention relates to a variable valve lift apparatus which varies lift of a valve by three steps.
Description of Related Art
Generally, an internal combustion engine receives fuel and air into a combustion chamber and generates power by combusting the fuel and the air. Herein, an intake valve is operated by drive of a camshaft, and air flows into the combustion chamber during when the intake valve is open. In addition, an exhaust valve is operated by drive of a camshaft, and air is exhausted from the combustion chamber while the exhaust valve is open.
Meanwhile, optimal operations of the intake valve or the exhaust valve are determined according to rotation speed of the engine. That is, lift and open/close timing of the valves are properly controlled according to rotation speed of the engine. A variable valve lift (VVL) apparatus has been developed in which the valves are operated for various lifts according to rotation speed of the engine for realizing optimal operations of the valves according to rotation speed of the engine. For example, there is a variable valve lift apparatus in which a plurality of cams for operating the valves by each different lift are provided to the camshaft, and the cam operating the valves is selected according to conditions.
When the plurality of cams are provided to the camshaft, however, the composition for selectively changing the cam to operate the intake valve or the exhaust valve may become complex, and interference between the elements of the composition may occur. Meanwhile, in case the plurality of cams are respectively and independently operated for preventing the interference between the elements of the composition, an additional constituent element is required as each cam for operating the cam such that the cost may be increased.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.